A communication network using a wireless communication system and most especially, a wireless communication network including a small microwave communication system of Point to Point is drawing attention as a means to complement an optical communication circuit or a wireless trunk line circuit. This kind of wireless communication network has wide use such as substitution or backup of a cellular phone network, communication between buildings and an optical communication network. Recently, as a communication system which links base stations in a mobile telephone network market which rapidly expands worldwide, its demand is growing greatly due to the characteristics such as cost performance of a device, easiness of construction, flexibility of system change and large capacity. As the demand of increase in high-speed and broadband for such communication grows, supply of cheaper and high-quality circuit service is being asked for. Also, with growing complexities of recent years' mobile network, reduction of operator's CAPEX (Capital Expenditure)/OPEX (Operating Expense) is required, and economization of a communication device and increase in efficiency of a network are required. Therefore, the technology which performs efficient route selection and the technology which performs circuit switching at the time of failure are essential and important. In a monitoring and control circuit which connects an NMS (Network Management System) which controls a network and an NE (Network Element), it is necessary to perform switching/route change flexibly/dynamically.
Among microwave communication systems, there is one which includes a function called AMR (Adaptive Modulation Radio). This AMR is the function to switch a transmission modulation method automatically according to the circuit condition of the wireless. By using this, in case the circuit condition is bad, using a transmission modulation method with low transmission rate, it is switched to the condition which raises reliability, and in case the circuit condition is good, using a transmission modulation method with high transmission rate, it is switched to the condition which secures communication capacity. The AMR function realizes modulation method switching hitless by judging at a receiving end, feeding back a modulation method which seemed most suitable to a sending end, and changing the modulation method successively from the sending end in units of a wireless frame.
It is effective to correspond to such dynamic changes in circuit transmission capacity, and to realize the function of monitoring and control circuit switching/route change between NMS-NE dynamically. However, route selection in the wireless communication network system which is a related technology is dependent on an existing routing protocol.
As a representative one of the existing routing protocols, for example, there is an RIP (Routing Information Protocol) of distance vector type. The RIP is a routing protocol which, in a communication network including a plurality of routers, and based on the number of hops (the number of routers to go through to reach the network), selects a route having the smallest numbers of hops. Each router sends a routing table (a correspondence table which shows a packet addressed to a certain network is transferred to which network next) which itself hold to a neighboring router. In the table, metrics for each network is indicated. The metrics is a numerical value which indicates a distance to the destination, and in case of the RIP, the number of hops to reach the network which is a target is used. The router which received the routing table adds, in case there is a network which itself did not know in the table, the network to the routing table which itself hold. Also, even in case itself knows the metrics, in case it is short, the information is added to the routing table of itself. By each router performing this operation, as the network as a whole, each router will hold the routing table by which it can be reached with the smallest number of hops.
Also, as a protocol which improved the RIP, there is an OSPF (Open Shortest Path First). While the RIP is a distance vector type, the OSPF is called a link state type. As one of the points which the OSPF is different from the RIP, there is a point that not the number of hops but “cost” of a network is used as the metrics. The cost is calculated based on a bandwidth of a circuit between two routers, and the cost value is defined to become smaller as the bandwidth becomes larger. By using this cost value, and by calculating the metric value which is a numerical value which becomes a standard for selecting the route from an original sending source to a destination, selection is made. Accordingly, in this case, a route with the low metric value will be the route which should be selected because its bandwidth is large.
In a relay network (communication network) including a plurality of relay stations and described in the following patent document 1, the main station searches relay routes of data from a sending source to a receiving destination, and determines the optimum route. By performing adaptive multistage relay using the determined route, good relay transmission is realized. As the standard of the optimum route search, either of a route where the total of the reciprocal of a CNR (Carrier to Noise Ratio) of each link is smallest or a route where the total of a BER (Bit Error Rate) of each link is smallest is used. Further, as the standard of the optimum route search, a route where the total of the packet loss ratio is smallest and a route where the number of relay stages is smallest are also used.